JP6590992B2 - Apparatus and method for detecting antenna coil - Google Patents

Description

The present invention relates to an apparatus and method for detecting an antenna coil having a detuning device that does not operate, and to a magnetic resonance tomography apparatus equipped with this type of apparatus. The detection device includes a transmitter, a transmission antenna, an amplitude measuring device, and a controller. The controller is configured to operate the transmitter to transmit a high-frequency signal having various predetermined amplitudes via the transmitting antenna, and obtains a test amplitude in response to the transmitted signal using an amplitude meter. Configured as follows.

  The magnetic resonance tomography apparatus is an imaging apparatus that images a test object by aligning the nuclear spins to be inspected with a strong external magnetic field, and precessing the nuclear spins by an alternating magnetic field and precessing about the alignment axis. It is. The precession or subsequent spin return from the excited state to the low energy state generates, in response, an alternating magnetic field that is received via the antenna.

  Spatial encoding is applied to these signals using gradient magnetic fields, which allows the received signals to be assigned to volume elements. The received signal is then evaluated to provide a three-dimensional image display for inspection. In order to receive such a signal, a local antenna, a so-called local coil, is preferably used, which is placed directly on the test object in order to achieve a good signal-to-noise ratio.

The local coil (antenna coil) is adjusted so as to resonate at the Larmor frequency, preferably the Larmor frequency of the hydrogen nucleus in the static magnetic field B0 of the magnetic resonance tomography apparatus for the reception. However, during excitation pulses for nuclear spins with the same frequency, the local coil needs to be detuned to avoid breakdown due to high induced voltages or large induced currents. First, the detuning is performed by an active element such as a PIN diode that is conducted by a control current. If the local coil is not connected, a passive protection mechanism such as an anti-parallel diode or fuse is provided. However, if this protection mechanism is defective, the local coil resonance conditions around the local coil result in excessive electromagnetic field strength during the excitation pulse, and this excessive field strength is generally in compliance with the global limit value. Despite this, it is a potential danger to the subject. In particular, there are cases where there are specific dangerous situations such as, for example, implants (in-vivo implants), and exceeding the electromagnetic field strength limit value is dangerous for the patient even for a short time.

A local coil provided with a monitoring device is disclosed in Patent Document 1, for example.

German patent application published: DE 10 2015 217 723 A1

  The object of the present invention is to make examinations using magnetic resonance tomography apparatus safer, especially for patients with implants.

The object is achieved by the apparatus of the present invention according to claim 1 , the magnetic resonance tomography apparatus according to claim 6 , and the method according to claim 7 .

The device of the present invention for detecting an antenna coil having a detuning device that does not operate includes a transmitter, a transmitting antenna, an amplitude measuring device and a controller. Preferably, the transmitter is configured to transmit a high frequency at a frequency of the Larmor frequency, and the antenna coil is configured to receive a magnetic resonance signal at the frequency. The antenna coil is, for example, a local coil or a body coil or one element of the coil.

The controller controls the transmitter to transmit a high-frequency signal from the transmitting antenna with various predetermined amplitudes (predetermined amplitudes). The amplitude preferably includes an amplitude that generates a voltage in the range of, for example, 0.1 V to 2 V, 0.2 V to 1 V, or 0.4 V to 0.8 V in an antenna coil that resonates within the effective range of the transmit antenna. . Preferably, the induced voltage includes a voltage that is in a non-linear region of a characteristic curve of a protective element such as a diode, a Zener diode or a PIN diode.

The controller is configured to communicate with the amplitude meter and to obtain the test amplitude with the amplitude meter in response to the transmitted signal. The inspection amplitude includes, for example, an amplitude proportional to the magnetic field component of the high-frequency signal that can be acquired by the imaging coil (pickup coil). For example, an amplitude corresponding to the electric field intensity that can be obtained by a dipole is also conceivable. Similarly, it may be the amplitude of either or both of the voltage and current in the feed line of the transmitting antenna. Then, for example, the amplitude of a signal that depends nonlinearly on current or voltage, such as power having a quadratic function, is also conceivable. Finally, it is also conceivable to acquire other variables such as phase via the amplitude by the controller. According to the present invention, “depending on the transmitted signal” means that the test amplitude is, for example, amplified, attenuated, filtered, mixed or mixed from an input signal that is generated in real time or near real time, for example by induction, according to the transmitted signal. It should be understood appropriately according to the context, in that it is derived by the usual steps at the time of reception in high frequency technology such as rectification. Preferably, the controller is configured to acquire at least two test amplitudes in response to the two predetermined amplitudes.

  Further, the controller is configured to determine a test relationship between the predetermined amplitude and the acquired test amplitude. For example, it is assumed that the controller creates a difference between both values of the predetermined amplitude and the acquired inspection amplitude or a quotient between the predetermined amplitude and the acquired inspection amplitude. Similarly, it is possible for the controller to process both values before or after in another step, for example applying a power function or logarithm to both values.

Finally, the controller is configured to compare the created inspection relationship with a predetermined reference relationship. For example, the controller checks whether the electromagnetic field strength increases linearly with the voltage applied to the transmitting antenna. It is assumed that the antenna coil with the protection diode enters the conduction region of the protection diode characteristic curve above the predetermined electromagnetic field strength, and as a result of the power absorbed by the antenna coil, there is no longer between the voltage of the transmitting antenna and the electromagnetic field strength. There is no linear relationship.

  The controller outputs a signal when it detects a corresponding deviation of a particular test relationship with respect to a predetermined reference relationship.

The device according to the invention makes it possible to detect an antenna coil with a detuning device that does not work before the antenna coil can be damaged by high RF power or before the patient is at risk.

  The magnetic resonance tomography apparatus according to the present invention and the method according to the present invention share the advantages of the apparatus according to the present invention.

  Other advantageous embodiments are set out in the cited claims.

In a possible embodiment of the device according to the invention, the amplitude measuring device comprises a directional coupler. Directional coupler, in order to obtain the power reflected by the transmitting antenna, preferably is disposed between the transmitter and transmitting antenna. The power reflected by the transmission antenna varies depending on the variable impedance of the transmission antenna caused by, for example, a resonator in the examination region. In this case, the inspection amplitude acquired in this aspect has dependence on the reflected power.

  Directional couplers are advantageous because they use unnecessarily counter-current high-frequency energy and provide a simple option to obtain information about the examination area associated with high-frequency radiation without resorting to prior effective transmit power. .

  In a possible embodiment of the device according to the invention, the predefined reference relationship is a linear relationship. The predetermined relationship can be stored in the memory of the controller, for example as a parameter set using a coefficient or value table. The linear relationship in this case is that the dependence between the predetermined amplitude and the test amplitude follows a linear equation of the form y = ax + b, or from this, it can be said that the range of measurement error is 1%, 5%, 10% at maximum, or It should be understood that this is only 20% off. It also includes special cases of linear relationships that are different from zero but constant.

  The electric and magnetic fields follow linear rules if there are no non-linear elements such as detuning due to diodes. Therefore, the comparison with the linear characteristic curve and the deviation thereof have the advantage that the appropriate safety technology and its proper functioning can be grasped.

In a possible embodiment of the device according to the invention, the controller is configured to determine the inspection relationship based on the phase of the inspection amplitude obtained by the amplitude measuring device. Accordingly, it is assumed that the predetermined amplitude is, for example, a voltage at a transmitter final stage (output stage) set by a drive signal of the controller. In this case, the current between the final stage of the transmitter and the transmission antenna may be acquired as the inspection amplitude by the amplitude measuring device. With respect to the impedance of the transmitting antenna having ohmic characteristics, the phase or phase relationship between voltage and current is constant, whereas a load due to a complex impedance such as a resonant oscillation circuit causes phase shift. If the complex impedance itself in this case is nonlinear and follows the transmitted power as in the case of a diode of a resonance circuit, for example, a nonlinear relationship also occurs with respect to the phase.

  There is an advantage that the protection device for the antenna coil can be detected with high sensitivity via the phase.

In a possible aspect of the apparatus according to the present invention, the controller is configured to determine the inspection relationship based on the power transmitted from the transmitting antenna. It is assumed that the amplitude measuring device in this case is configured to obtain electric power by obtaining a current and a voltage and calculating a product of the voltage and the current. However, it is also possible to calculate the power from one of the two values, assuming that the impedance is almost constant. This is particularly envisaged when the change in the measured value is slight, i.e. for example smaller than 5% or 10%. For example, this is possible when the transmitting antenna is substantially matched with the impedance of the feeder line and the inspection amplitude is reflected power generated only when the matching changes. Finally, basically, it is also possible to obtain power directly, for example with a bolometer.

  Power is an advantageous variable that can obtain a power sink in the form of an antenna coil, regardless of the phase position, which may depend on the location between current and voltage.

  In a possible embodiment of the device according to the invention, preferably the controller is configured to block high-frequency delivery by the transmitter according to the output signal.

The device according to the invention has the advantage that the high-frequency transmission by the transmitter can be controlled, for example interrupted, before damage occurs, for example when an unconnected antenna coil is arranged in the examination range.

In a possible aspect of the device according to the invention, the device is configured to send a plurality of different default modes from the transmitting antenna. The antenna is assumed to be, for example, an array including a plurality of individual transmission elements, and the transmission elements can be individually driven by a transmitter using a distribution matrix. It is also possible to provide a plurality of independent transmission modules in the transmitter. This type of transmission array can be provided in a body coil comprising a plurality of transmission elements or in a local coil comprising a plurality of coil elements. If the different modes have different polarizations, it is envisaged that the individual modes excite the antenna coil with little or no excitement in the relevant alignment of the antenna coil. In this aspect, an apparatus according to the present invention is configured to acquire a plurality of inspection amplitudes by a plurality of amplitude measuring devices and determine one or more inspection relationships based on the acquired inspection amplitudes. A single amplitude measuring device having a multiplexer with multiple inputs for the input to be acquired can also be interpreted as multiple amplitude measuring devices.

The device according to the present invention also has the ability to obtain test amplitudes for various modes, and for this purpose can also detect antenna coils in various orientations with respect to the transmitting antenna.

  In a possible embodiment of the magnetic resonance tomography apparatus according to the invention, the transmitter is configured to generate excitation pulses for nuclear spins. In particular, the transmitter has a required delivery power of, for example, greater than 1 kilowatt to excite nuclear spin to a sufficient extent.

The apparatus according to the present invention detects an unconnected antenna coil (for example, an antenna coil in the form of a local coil) using the existing basic structure of a magnetic resonance tomography apparatus including the transmitter and a transmission antenna (for example, a body coil). can do.

  In a possible embodiment of the method according to the invention, the method comprises the step of stopping the antenna coil detuning device. For example, if the controller cuts off the power supply to the PIN diode or other switching element of the antenna coil, the PIN diode or other switching element will no longer short-circuit the resonance circuit. In this case, the antenna coil exists in a range having an appropriate electromagnetic field strength of the high-frequency signal when the transmitter is operated. Particularly suitable electromagnetic field strength here is the electromagnetic field strength of a high-frequency field that produces a voltage exceeding 0.5 V or 1 V in a resonance circuit without attenuation of the antenna coil.

  Using the apparatus according to the present invention, in the above method, not only the unconnected antenna coil can be detected, but also the function of the detuning device can be checked in the connected antenna coil. This applies in particular to passive additional protection devices that operate without external drive, such as fuses or antiparallel diodes.

  Through the embodiments described in detail below with reference to the following drawings, the above-mentioned characteristics, features and advantages of the present invention, and techniques for achieving them will be clarified.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the magnetic resonance tomography apparatus which concerns on this invention provided with an example of the apparatus based on this invention. 1 is a schematic diagram showing an embodiment of an apparatus according to the present invention. 1 is a schematic diagram showing an embodiment of an apparatus according to the present invention. 6 is a flowchart outlining an example of a method according to the present invention.

  FIG. 1 shows a schematic diagram of a magnetic resonance tomography apparatus 1 according to an embodiment of the present invention.

  The magnet unit 10 includes a field 11 that generates a static magnetic field B0 that aligns nuclear spins of a subject (for example, a patient) 40 in an imaging region. The imaging region is set in the patient tunnel 16, and the patient tunnel 16 extends through the magnet unit 10 in the long axis direction 2. In general, the superconducting magnet included in the field 11 can provide a magnetic field having a magnetic flux density of up to 3 T, which is higher than that in the latest apparatus. However, for smaller magnetic field strengths, permanent magnets or electromagnets with normal conducting coils can also be used.

  Furthermore, the magnet unit 10 includes gradient magnetic field coils 12 that superimpose a variable magnetic field on the magnetic field B0 in three spatial directions for spatial differentiation of the image area acquired in the examination volume. Configured. The gradient coil 12 is generally a coil made of a normal conducting wire, and the normal conducting wire can generate magnetic fields orthogonal to each other in the inspection volume.

  The magnet unit 10 similarly has a body coil 14, which radiates a high frequency signal supplied via a signal line into the examination volume, receives a resonance signal emitted from the patient 40, and receives a signal. Output via line. Preferably, the body coil 14 is replaced with a local coil 50 for high frequency signal reception, which is located in the patient tunnel 16 near the patient 40. However, it is also conceivable to configure the local coil 50 to transmit and receive.

  The control unit 20 supplies various signals for the gradient magnetic field coil 12 and the body coil 14 to the magnet unit 10 and evaluates the received signals.

  The control unit 20 includes a gradient magnetic field controller 21 configured to supply a variable current to the gradient coil 12 through a power supply line, and the variable current is supplied to the inspection volume in a time-adjusted manner. A predetermined gradient magnetic field is provided.

  Further, the control unit 20 has a high frequency unit 22, which has a predetermined high frequency characteristic, amplitude, and spectral power distribution in order to excite the magnetic resonance of the nuclear spin in the patient 40. Generate a pulse. In this embodiment, pulse power in the kilowatt range can be obtained.

  FIG. 2 illustrates an embodiment of the device according to the invention. 2, the same reference numerals as those in FIG. 1 are given to the same components as those in FIG. For clarity, not all of FIG. 1 is shown.

The high frequency unit 22 is provided with a transmitter 24 for generating an excitation pulse having a Larmor frequency of the magnetic resonance tomography apparatus. Preferably, the Larmor frequency includes a Larmor frequency of a hydrogen nucleus in the magnetic field B0 of the field 11, but may be a nucleus of another element. The transmitter 24 is controlled by the controller 23 of the magnetic resonance tomography apparatus 1 via the signal bus 26, thereby having any one or more of a predetermined frequency, phase, spectrum distribution, and power (output). An excitation pulse is generated, and the excitation pulse is transmitted to the body coil 14 as a transmitting antenna via a signal link. In this embodiment, the controller 23 and the transmitter 24 are configured to adjust a wide range of power ranging from several watts to several kilowatts. In particular, the power of the transmitter 24 can be reduced to the extent that it is not dangerous for the patient and to the extent that the unconnected antenna coil (here local coil 50) is not damaged.

  An amplitude measuring device 25 is disposed between the transmitter 24 and the body coil 14, and the amplitude measuring device 25 can acquire a measured value of the output signal of the transmitter 24. This is, for example, either or both voltage and current. An example is also possible in which the amplitude measuring device 25 does not directly acquire power by the action of the amplitude measuring device 25 such as a bolometer, but acquires it by acquiring and multiplying current and voltage.

  FIG. 3 shows a modification of the device according to the invention, in which the transmitter 24 has a plurality of transmission modules capable of generating high-frequency signals independently of each other, for example independent of each other. Various modes with different spatial distributions and polarizations can be implemented by the body coil 14 having a plurality of radiating elements. This scheme also allows different modes to excite the local coil 50. The coil windings of the local coil 50 are aligned in a direction orthogonal to the first mode, and therefore are not excited in the first mode. In this example, the plurality of amplitude measuring devices 25 each acquire the inspection amplitude of the transmission module. In another example, a multiplexer may be used to provide one amplitude measuring device 25 that receives the test amplitude of each transmission module.

The amplitude measuring device 25 may also include, for example, a directional coupler that enables acquisition of power reflected by the transmitting antenna.

  FIG. 4 is a flowchart outlining a possible embodiment of the method according to the invention.

In step S <b> 20, the controller 23 issues a command to the transmitter 24 via the signal bus 26, and causes high-frequency signals having various predetermined amplitudes to be transmitted from the transmission antenna, for example, the body coil 14. The amplitude at this time is chosen so that the antenna coil, for example the local coil 50 and in particular the patient is not dangerous. For example, the power is less than 5 watts, 10 watts or 100 watts, and the voltage induced in the resonant unattenuated antenna coil is less than 1V, 2V or 5V.

In step S30, the amplitude measuring device 25 acquires the inspection amplitude according to the transmitted signal. In the embodiment of FIG. 3, this is, for example, the voltage on the signal line leading to the transmit antenna. In addition, the voltage and current are acquired by the amplitude measuring device 25, or either or both of the power reflected from the transmitting antenna and the power flowing to the antenna are acquired by the amplitude measuring device 25 including a directional coupler. It is also possible to do. The amplitude measuring device 25 can further acquire a signal processed by digital or analog signal processing such as rectification or filtering, and the signal follows the signal transmitted from the transmitter 24, and the power of the signal is Or related to the phase of the signal. The main point regarding the acquired signals is that these signals enable estimation of the high frequency characteristics in the patient tunnel 16 or are influenced by the high frequency characteristics.

  Step S20 and step S30 are preferably repeated with different amplitudes. For example, starting from a small predetermined amplitude of the signal to be transmitted, the amplitude can be increased in steps, for example at regular intervals or exponentially. According to this method, it is possible to start from a weak and safe electromagnetic field strength. In order to later distinguish between a linear increase and a non-linear increase in the test signal, it is necessary to repeat at least three times with different default amplitudes, but the possible measurements with a default amplitude of zero can be omitted.

  In step S40, the controller 23 determines the inspection relationship between the predetermined amplitude and the acquired inspection amplitude. However, a dedicated analog or digital signal processing unit may perform this step. In the simplest example, the controller 23 creates a quotient from each predetermined amplitude and its associated test amplitude for this purpose. This quotient represents the slope of a linear relationship. According to Maxwell's law, the predicted relationship between electrical and magnetic variables is initially linear. The relationship departs from the linear relationship only when a non-linear element such as a protection diode is coupled to the alternating electromagnetic field and the induced voltage is in the non-linear region of the characteristic curve of the element.

In step S50, for example, when the controller 23 confirms that the determined inspection relationship deviates from the predetermined reference relationship, the controller 23 outputs a signal. In the simplest example, the reference relationship is a linear relationship that reflects a predicted linear relationship between the default output amplitude and the test amplitude. However, the non-linearity of the amplitude measuring device 25 can also be taken into account in advance in the reference relationship, so that this reference relationship at least partly follows, for example, the transition of a power function or an exponential function. This is caused by the characteristics of the rectifier diode in the amplitude measuring device 25, for example. A signal is generated only when the determined relationship deviates from the predicted characteristic (behavior). Since the antenna coil which is not detuned in this case is suspected to be present in the patient tunnel, preferably generated signal is a transmitter 24 control or at least reduce blocking further transmission of high frequency power by It will be used for.

  In step S10, which is possible in the embodiment of the method according to the invention, the controller 23 stops the antenna coil detuning device. The antenna coil is, for example, a local coil 50, and the detuning device is stopped by cutting off the supply voltage to the PIN diode that short-circuits the resonance circuit having the coil winding of the local coil 50 in the local coil 50. Thereby, the local coil 50 is resonance-coupled with the high frequency radiated from the body coil 14 by the transmitter 24, and takes out electric power from the high frequency field. At this time, the passive protection mechanism such as an antiparallel diode in the local coil 50 prevents the generation of an excessive voltage in the local coil 50 due to the increase in power in the high frequency field due to its nonlinear characteristic curve. The power drawn from the high frequency field also increases exponentially, so in the simplest case, the non-linear relationship between the predetermined amplitude and the test amplitude results in the presence of the antenna coil and its passive protection mechanism functioning without problems. The recognition that it is.

  Although the present invention has been described in detail using preferred exemplary embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art will be able to make other modifications outside the protection scope of the present invention. Can be derived without any problems.

DESCRIPTION OF SYMBOLS 1 Magnetic resonance tomography apparatus 10 Magnet unit 11 Field 12 Gradient magnetic field coil 14 Body coil 16 Subject tunnel 20 Control unit 21 Gradient magnetic field control apparatus 22 High frequency unit 23 Controller 24 Transmitter 25 Amplitude measuring device 26 Signal bus 50 Local coil

Claims (10)

A device for detecting an antenna coil having a detuning device that does not operate ,
A transmitter (24), a transmission antenna, an amplitude measuring device (25), and a controller (23);
The controller (23)
Controlling the transmitter (24) to transmit a high frequency signal from the transmitting antenna with various predetermined amplitudes;
In accordance with the transmitted high-frequency signal, an inspection amplitude is acquired by the amplitude measuring device (25),
Determining an inspection relationship between the predetermined amplitude and the acquired inspection amplitude;
When the determined inspection relationship deviates from a predetermined reference relationship , the transmitter (24) is configured to control transmission of a high-frequency signal ,
The apparatus wherein the predetermined reference relationship in the controller (23) is a linear relationship.   The apparatus of claim 1, wherein the amplitude measuring device (25) comprises a directional coupler and is configured to acquire the inspection amplitude in response to reflected power.   The apparatus according to claim 1 or 2, wherein the controller (23) is configured to determine the inspection relationship based on the phase of the inspection amplitude obtained by the amplitude measuring device (25). The apparatus according to any one of claims 1 to 3, wherein the controller (23) is configured to determine the inspection relationship based on power transmitted from the transmitting antenna. A plurality of different predetermined modes are transmitted from the transmission antenna, a plurality of inspection amplitudes are acquired by the plurality of amplitude measuring devices (25), and one or more inspection relations are determined based on the acquired inspection amplitudes. The device according to claim 1 , wherein the device is configured. A magnetic resonance tomography apparatus having the apparatus according to claim 1 ,
Magnetic resonance tomography apparatus, wherein the transmitter (24) is configured to generate excitation pulses for nuclear spins. A method for detecting an antenna coil having a detuning device that does not operate using the device of any one of claims 1-5 ,
Controlling the transmitter (24) by the controller (23) so that the transmitter (24) transmits high-frequency signals having various predetermined amplitudes from the transmitting antenna;
Acquiring an inspection amplitude by the amplitude measuring device (25) according to the transmitted high-frequency signal (S30);
Determining an inspection relationship between the predetermined amplitude and the acquired inspection amplitude (S40);
(S50) controlling the transmission of a high-frequency signal by the transmitter (24) when the determined inspection relationship deviates from a predetermined reference relationship,
The method wherein the predetermined reference relationship in the controller (23) is a linear relationship. A step (S10) of stopping the antenna coil detuning device;
The method according to claim 7 , wherein the antenna coil is arranged in a region having an appropriate electromagnetic field strength of the high-frequency signal in the step (S20) of controlling the transmitter (24). A computer program that can be loaded directly into the processor of the programmable controller (23),
Computer program comprising program code means for executing all the steps of the method according to claim 7 or 8 when executed in said controller (23). A computer-readable storage medium storing electronically readable control information,
The control information is configured to execute the method according to claim 7 or 8 by using the storage medium in the controller (23) of the magnetic resonance tomography apparatus (1) according to claim 6. Storage medium.